1. Field of the Invention
The present invention relates to a polishing plate for polishing a workpiece by rubbing the workpiece to be polished with it, specifically a polishing plate for smoothing a hard material such as a diamond like carbon and the like.
2. Description of the Related Art
A diamond like carbon (DLC), silicon carbide (SiC), silicon nitride (SiN), silicon (Si) or the like has been frequently used as an electronic material. Particularly, since DLC has characteristics similar to a diamond and further there can be obtained a thin film thereof which is dense and large in area as compared to that of diamond, it is expected that DLC is used for various purposes as functional materials. As a practical use, for example, it has been considered that DLC is used as a protection film for a magnetic disk, a protection film for an optical component, and the like.
These electronic materials have Knoop hardness (kgf/mm2) of about 2000-5000 for DLC, about 3000-4000 for SiC, about 1800 for SiN and about 1200 for Si, respectively, and thus each of them is very hard.
For example, a DLC film formed on a magnetic disk surface is necessary to be smoothed in practical use. Conventionally, a DLC film has been smoothed by rubbing a surface thereof to be polished with a resin pad soaked with a polishing agent containing particles such as synthetic diamond, SiC, SiN, or SiO2 and dispersion medium.
However, in this method, since the polishing agent is easy to escape and is not uniformly applied to the surface to be polished, there are problems that uniformity in the processed surface is bad and its processing efficiency is also bad.
Alternatively, it is suggested that polishing is performed using a polishing tool wherein synthetic diamond particles is adhered to a substrate by an adhesive or by an electrolytic method. However, synthetic diamonds, which have minute particle sizes possible to smooth surface roughness of a surface to be polished to 50 nm or less in Ra, are difficult to be uniformly adhered to a substrate, still less it is impossible to prepare a tool having a size of 50 mm or more in diameter, which can correspond to polishing of a material having a large area. Additionally, synthetic diamond particles having a minute size used as a material in themselves are expensive and process for adhering is complicated, so that there is also a problem in terms of a production cost of the tool.